Deviation detecting apparatus

ABSTRACT

A deviation detecting apparatus having a primary coil for generating an alternating magnetic field, and a secondary voltage inducing device disposed to oppose said primary coil with a space therebetween and producing a secondary voltage in accordance with the alternating magnetic field caused by said primary coil. In this case, said secondary voltage inducing device consists of four secondary coils, said four secondary coils being arranged in square and made up by winding two electrically insulated wires in parallel, the two first wires of the adjacent two secondary coils being connected to deliver as an output a sum or difference of induced voltages therein and to form two pairs of winding groups each of said two pairs of winding groups being connected to deliver as an output a sum or difference of induced voltages therein, the two adjacent second wires being connected to deliver as an output a sum or difference of induced voltages therein and to form two pairs of winding groups in a different manner to that in said first wires, said pairs of winding groups being connected in such a manner that a sum or difference of induced voltages therein is delivered as an output.

United States Patent 1 Hojo et a1.

[ DEVIATION DETECTING APPARATUS [75] Inventors: Takeshi Hojo,Fujisawa-shi;

Shin-[chi Kawada, Yokohama-shi, both of Japan V [73] Assignee:Kabushikikaisha Tokyo Keiki (Tokyo Keiki Co., Ltd.), Tokyo, Japan [22]Filed: Aug. 2, 1972 [21] Appl. No.: 277,399

[30] Foreign Application Priority Data Aug. 10, 1971 Japan 46/60499 Aug.10, 1971' Japan 46/60497 [52] US. Cl 336/182,336/121, 336/122, 336/126[51] Int. Cl 1101f 27/28, 1-101f 21/04 [58] Field of Search 336/115,116, 121, 336/122,123,l24,125,126, 30,180,182

[56] References Cited UNITED STATES PATENTS 2,458,700 1/ 1949 Greenough336/122X 2,455,672 12/1948 Greenough 336/125 2,282,060 5/1942 James etal. 336/125 2,271,517 2/1942 Cockerell 336/125 X 1,556,612 10/1925Kloneck 336/123 X 2,174,017 9/1939 Sullinger et al 336/125 X Nov. 6,1973 1,426,137 8/1922 Wright 336/125 X 2,373,206 4/1945 Thomas 336/123 XPrimary Examiner-Thomas J. Kozma Attorney-Benjamin 11. Sherman et a1.

['57] ABSTRACT A deviation detecting apparatus having a primary coil forgenerating an alternating magnetic field, and a secondary voltageinducing device disposed to oppose said primary coil with a spacetherebetween and producing a secondary voltage in accordance with thealternating magnetic field caused by said primary coil. in this case,said secondary voltage inducing device consists of four secondary coils,said four secondary coils being arranged in square and made up bywinding two electrically insulated wires in parallel, the two firstwires of the adjacent two secondary coils being connected to deliver asan output a sum or difference of induced voltages therein and to formtwo pairs of winding groupseach of said two pairs of winding groupsbeing connected to deliver as an output a sum or difference of inducedvoltages therein, the two adjacent second wires being connected todeliver as an output a sum or difference of induced voltages therein andto form two pairs of winding groups in a'different manner to that insaid first wires, said pairs of winding groups being connected in such amanner that a sum or difference of induced voltages therein is deliveredas an output.

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' SHEU HF PATENTEDNBY 8|973 3771.085 SHEETSCF e DEVIATION DETECTINGAPPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Theinvention relates to a deviation detecting apparatus which converts amechanical displacement or deviation into a corresponding electricalsignal with, for example, a differential transformer.

2. Description of the Prior Art A conventional deviation detectingapparatus has the drawback that it is low in detecting accuracy.

SUMMARY OF THE INVENTION It is an object of the invention to provide adeviation or displacement detecting apparatus free from thedrawback-encountered in the prior art.

It is another object of the invention to provide a deviation ordisplacement detecting apparatus which detects a deviation positivelyand accurately.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram showing adeviation detecting apparatus of the prior art;

FIG. 2A is a side view of its secondary coil;

FIG. 2B is a plane view of the secondary coil depicted in FIG. 2A;

FIG. 3A is a side view of a secondary coil of a deviation detectingapparatus of another conventionalapparatus;

FIG. 3B is its plane view;

FIG. 4 is a plane view of a deviation detectingapparatus according tothe invention;

' FIG. 5 is a perspective view, partialy cut away, of a gyrocompassequipped with a deviation detectin'gapparatus of the invention;

FIGS. 6, 7 and 8 are schematic diagrams for explaining a deviationdetecting apparatus of the invention used in the gyrocompass andafollow-up systememployed therein;.

FIG. 9 is a schematic diagram showing a tank used in the gyrocompass;

FIG. 10 is aschematic diagram of a damping device equipped with anotherdeviation detecting apparatus'of the invention; and

FIG. 1 l is a plane view showing another embodimentof the deviationdetecting apparatus .of the invention.

DESCRIPTION OF THE PREFERRED- EMBODIMENTS which generates alternatingmagnetic'fields or fluxes-B:

and B in a space when excited withan AC power source 103. Thedifferential transformer has a secondary coil assembly 102 whichconsists of two secondary coils 102a and 102b, the secondary coils 102aand. 102b being connected with each other differentially or inadifferential manner. When the secondary coil assembly 102 is positionedwith respect to the primary coil 10.1, the magneticfluxes B and Bgenerated by the primary coil 101 passthrough the secondary coils 102aand 102b equally. Accordingly, voltages induced in the secondary coils102a and 102b by the magnetic fluxes B and B are equal in magnitude anddirection. In this case, the secondary coils 102a and 102b are connecteddifferentially, so that there is produced no voltage at an outputterminal 104 of the secondary coil assembly 102. However, if thesecondary coil assembly 102 is moved to the x-direction in the figurewith respect to the primary coil 101 which is assumed to be fixed, themagnetic flux passing through the secondary coil 102a increases ascompared with that passing through the secondary coil 102b with theresult that there is derived at the output terminal 104 a voltage whichcorresponds in magnitude to the moving distance or displacement of thesecondary coil assembly 102 relative to the primary c'oil 101. If thesecondary coil assembly 102 moves to the counter direction, namely tothe x'-direction in the figure with respect to the primary coil 101,there is derived at the output terminal 104 a voltage which correspondsin magnitude to the moving distance of the secondary coil assembly 102relative to the primary coil 1'01 and is reversed in phase, namely isshifted in phase by 180 with that of the former. In this case, there maybe provided an iron core or ferromagnetic core for enhancing themagnetic flux.

FIGS. 2A and 2B show the case where the secondary coil assembly 102consisting of two coils 102a and 102b is fixedly mounted on a base plate105 made of insulating material with a bonding agent or the like.

FIGS. 3A and 3B show the case where the secondary coil assembly 102 madeof secondary coils 102a, 102b, 102c and 102d mounted on the base plate105 on its one surface 105a. The deviation detecting apparatusconsisting of the secondary coil assembly 102 and the primary coil 101shown in FIGS. 3A and 33 may detect movement of, for example, thesecondary coil assembly 102 with respect to the primary coil 101 in x-,x'-, yand y'- directions.

In the example of FIGS. 3A and 3B, the primary coil 101 is wound insubstantially square-shape and excited by AC current. One pair of thesecondary coils 102a and 102d are mounted on the other pair of thesecondary coils 102a and l02hwith a rotation angle, of 90 with respectto the latter. The coils of the two pairs are connected differentiallyor in a differential manner, so that at an output terminal 104x of thecoils 102a and 102b there is delivered a voltage corresponding to themoving distance thereof in the x-x direction relative to the primarycoil 101 and at an output terminal 104y of the coils 1020 and 102d thereis delivered a voltage corresponding to the moving distance thereof inthe y-y direction relative to the primary coil 101. In this case, ifeach of the coils is wound rectangular and the area of the primary coil101 is selected smaller than those-- of the two secondary coils, theinterference therebeence in gap between the primary coil 101 and thesecondary coils 102a and 102b and in gap between the primary coil 101and the secondary coils 102c and 102d because of the thickness of thecoils results in the dif- V more distance with respect to the primarycoil 101 than that of the secondary coils 102a and 102b with respect tothe primary coil 101, the pickup gain, namely the output voltage perunit displacement in y-y direction is smaller than that in x-x'direction.

A description will be now given on an embodiment of the deviationdetecting apparatus of the invention, which is free from the drawbackencountered in the prior art, with reference to FIG. 4. In the inventionshown in FIG. 4, a deviation detecting apparatus referred at 100generally is made in a differential transformer which consists of aprimary coil 110' and a secondary coil assembly 1 10. The secondary coilassembly 110 consists of, for example, four coils I11, 112, 113 and 114each of which is wound in square. All the secondary coils 111 to 114 aremounted on a base plate 115 made of insulating material in such a mannerthat they are substantailly in the same plane and form a square as awhole, as shown in FIG. 4. In this case, the respective secondary coils111 to 114 are made with two windings electrically insulated with eachother. In FIG. 4, the first winding for forming each secondary coil isshown by references with the corresponding reference numerals with a,the second winding for forming each secondary coil is shown byreferences with the corresponding reference numerals with b and thestarting and terminating ends of the respective windings are shown byreference with thecorresponding numerals with s and F, respectively.Accordingly, sixteen wires lllas, lllaF, lllbs, lI1bF,. l14bs, and 114bF are led out from the secondary coils 111 to 114, as shown in FIG. 4.In the example of FIG. 4, the first windings, namely those referred atreferences with a suffix a are used for detecting the deviation ordisplacement in the y-y' direction, while the second windings, namelythose referred at references with a suffix b are employed for detectingthe deviation or displacment in the xx' direction. If the first windingsfor secondary coils 111a and 112a, and those for the secondary coils113a and 114a are connected with one another to produce a sum output,they correspond to the secondary coils 112d and 1120 in FIG. 3.Therefore, if they are further connected differentially or in adifferential manner, a voltage corresponding to the moving distance inthe y-y direction may be obtained across the wires lllas and 1l3as.Meanwhile, if the second windings for the secondary coils 1l1b and ll3band those for the secondary coils 112 b and ll4b are connected with oneanother to produce an sum voltage, they correspond to the secondarycoils 112a and l12b. Therefore, if they are further connecteddifferentially, a voltage corresponding to the moving distance in thex-x direction may be obtained across the wires ll3bs and 1l4bs. Asapparent from the foregoing description, it will be clear that thediviation detecting apparatus of the invention can detect the movingdistances in both the y-y and x-x' directions.

Further, in the invention the first and second windings are made up bytwo elementary wires electrically insulated with each other, so that thegaps between the primary coil and the secondary coils are same in lengthand the pickup gain in x-x' and y-y' directions is stricly same.Accordingly, it will be apparent that the deviation detecting apparatusof the invention can detect the moving distance or deviation in twomutually perpendicular directions positively and accurately.

A description will now be given on a gyrocompass in which the deviationdetecting device according to the invention, as described above, isemployed as a noncontact type deviation detecting apparatus or a pickupfor following-up, with reference to FIG. 5.

In FIG. 5, reference numeral 1 indicates a gyro case housing therein agyro rotor rotating at high speed, which case is formed in aliquid-tight manner. Reference numeral 2 designates a container such asa tank which contains the gyro case 1, and 3 a suspension wire forsupporting the gyro case 1, which wire is fixed at the upper end to thetank 2 and at the'lower end to the gyro case 1 respectively. Referencenumerals 4N, 4S and SN, 58 identify primary and secondary sides ormembers of a non-contact deviation detecting device 6 respectively. Themembers 4N, 5N and 48, 5S correspond to the primary coil 110 and thesecondary coil assembly 110 of the apparatus of the invention. Theprimary sides 4N and 48 are positioned on, for example, the surface ofthe gyro case 1 at the intersections of the surface of the gyro case 1with the extension of the spin axis of the gyro, that is, on the northand south sides of the gyro, while the secondary sides 5N and 58 aredisposed on the tank 2 in alignment with the primary sides 4N and 48.Reference numeral 7 denotes a liquid such as a damping oil of highviscosity, for example, a silicon oil which is contained in the tank 2.A pair of horizontal shafts 8 and 8' are attached at their one ends tothe tank 2 on the equator thereof at positions perpendicular to the spinaxis of the gyro and are rotatably fitted at the other ends intobearings 13 and 13 which are disposed on a horizontal ring 12 inalignmentwith the horizontal shafts 8 and 8'. Reference numeral 10represents a servo motor for horizontal follow-up, which is attached tothe horizontal ring 12. A horizontal gear 9 is mounted about the one ofthe horizontal shafts, for example, shaft 8 and is meshed with ahorizontal pinion 11 attached to the rotary shaft of the servo motor 10.Gimbal shafts 14 and 14' are attached to the horizontal ring 12 atpositions perpendicular to the aforesaid horizontal shaft bearings 13and.

13' and these gimbal shafts l4 and 14' are rotatably supported by gimbalbearings 15 and 15' provided on a follow-up ring 16 in alignment withthe shafts 14 and 14' respectively. Follow-up shafts 17 and 17 aresecured at one ends thereof to the bottom and top of the follow-up ring16 and their free ends are rotatably inserted into follow-up shaftbearings 25 and 25 disposed on a binnacle 24 at positions correspondingthereto respectively. An azimuth gear 21 is mounted about the one of thefollow-up shafts, namely, the shaft 17 in the example. Reference numeral19 designates an azimuth follow-up servo motor attached to the binnacle24 and 20 an azimuth pinion affixed to the rotary shaft of the servomotor 19, which pinion meshes with the azimuth gear 21. Referencenumeral 22 indicates a compass card secured to the follow-up shaft 17'.Reference numeral 23 represents a reference line plate disposed on thetop of the binnacle 24 in association with the compass card 22. Thecourse of the ship equipped with the gyrocompass is read out from thecombination of a reference line 26 drawn on the plate 23 centrallythereof and the compass card 22.

Referring now to FIGS. 6, and 7, a descriptionwill be given of oneconcrete example of the aforementioned non-contact deviation detectingdevice 6 or 100. It should be noted that each of the secondary coils arepractically made by two wires wound together to be four coils as shownin FIG. 4, butfor the sake of brevity those shown in FIG. 3 are employedin the following.

FIG. 6 shows the pair of N (north) sidesthereof. As shown in the figure,the primary side 4N. is a coil and its winding lies in a planeperpendicular to the spin axis of the gyro and this coil is usuallyexcitedby'AC current from a gyro power source PS, establishingalternating magnetic fields indicated by broken arrows a and a Thesecondary side SN is made up of four rectangular coils SNW, SNE, SNU andSNL and theone'pair of coils SNW and SNE are disposed side by side andthe other pair of coils SNL and SNU are disposed one above the other.The winding starting ends of the pair of coils SNW and SNE and those ofthe other pair of I coils SNU and SNL are interconnected. Assuming thatthe primary side coil 4N, that is, the gyro case 1 lies at the center ofthe secondary side coil SN, that is, the tank 2, a magnetic fluxproduced by the primary coil 4N passes through the secondary coils SNW,SNE,

tion of the gyro case 1. This output voltage is applied to a controlwindingof the azimuth servo motor 19 through a servo amplifier 30 (whichmay be omitted). The revolution of the servo motor 19 is transmitted tothe tank 2 through the azimuth pinion 20, theazimuth gear 21, thefollow-up ring 16 and the horiziontal ring SNU and SNL to induce acorresponding voltage in each of them. However, the magnetic flux ineach secondary coil is substantially equal to that in the other coilsand the respective pairs of coils are connected in a differential manneras described above, so that no voltage is derived at their outputterminals 2-1 and 22. Assuming that the primary coil 4N is displacedeastward (indicated by E in the figure), the magnetic flux passingthrough the coil .SNE increases while that passing through the coil SNWdecreases, so that a voltage is derived at the output terminal 2-1 butno output is derived at the terminal 22. While, when the primary'coil 4Nis displaced westward (indicated byW in the figure), the induced voltageof the coil SNW increases, while that of the coil SNE decreases,deriving at the output terminal 21 a voltage opposite in phase. to thatobtained when the primary coil 4N is displaced eastward. In this case,since the coils SNU and SNL are arranged in a vertical direction, novoltage is produced at the output terminal 2-2 as in the above case.While, in response to the vertical displacement of the primary coil4N,equal voltage is induced in the coils SNW and SNE arranged side by side,but an unequal voltage is induced in the coils SNL and SNU disposed inthe vertical direction, so that an output voltage is provided at outputterminal 22. Namely, with the constructionshown in FIG. 6, it ispossible to detect the displacement of the gyro case 1 in the east-westdirection and in the vertical direction relative to the tank 2 on thenorth end.

FIG. 7 illustrates a device for detecting the displacement of the gyrocase in the east-west direction only, with the gyro case 1 being viewedfrom above. Namely, the non-contact deviation detecting device on thesouth side ismade up of the primary side coil 48 and secondary sidecoils SSE and SSW. When the gyro case -l is displaced eastward, themagnetic flux passing through the coil SSE increases and that passingthrough the coil SSW decreases to induce a voltage between terminals 3-1and the phase of the voltage is the same 12 to control the tank 2 insuch a manner as to reduce the angular deviation between the tank 2 andthe gyro case 1 about the aforesaid vertical axis 0 to be zero. Namely,in whatever azimuth the gyro case 1 may lie, the suspension wire 3 iscompletely prevented by the servo system from twisting and any externaldistrubance torque is impressed from the suspension wire 3 to the gyroabout the vertical axis. In FIG. 7, reference numeral 3-3 indicates anerror correcting signal generator, which produces a voltagecorresponding to the speed or latitude of the ship to make thecorresponding angular offset in the follow-up system, by which thesuspension wire 3 is twisted to apply torque to the gyro about itsvertical axis, thus correcting an error.

I FIG. 8 illustrates a horizontal follow-up system, in which the coilsSNU, SNL and SSU, SSL of the secondary sides SN and SS are alsointerconnected in a differential manner as in the former case, so thatno output voltage is produced between terminals 4-1 of the coils SNU andSNL in response to the vertical movement of the gyro case 1 relative tothe tank 2 but a voltage is derived between the terminals 4-1 inresponse to the angular movement of the gyrb case 1 about a horizontalaxis 0' and the voltage produced is applied directly or through a servoamplifier 31 to. a control winding of the horizontal follow-up servomotor 10. The rotation of the horizontal follow-up servo motor 10 istransmitted through the horizontal pinion 11 and the horizontal gear 9to the tank 2 to turn it, reducing its angular deviation between thetank2 and the gyro case 1 to be zero.

' FIG. 9 schematically shows theinside of the tank 2 in the case wherethe north-seeking end A (lying on the gyro case 1) of the extension ofthe spin axis of the gyro in the gyro case 1 is inclined up at an angle0 to a horizontal plane I-I-H'. In the figure, reference character 0indicates the center of gravity of the gyro case 1, Q the coupling pointof the suspension wire 3 with the gyro case l, P the coupling point ofthe suspension wire 3 with the tank 2, and 0 the center of the tank 2.Assume that the spin axis of the gyro rotor in the gyro case 1 ishorizontal (6=0), O and O coincides with each other. Reference characterA designates the northseeking end and B a point on the gyro case 1 whichis diametrically opposite to the north-seeking end A, and A and B pointson the tank 2 corresponding to A and B. Since the suspension wire 3 hasflexural rigidity in practice, it presents a deflection curve such asindicated by a broken line in the figure. Accordingly, the amount ofaxial movement e (0 0 of the gyro case 1 relative to the tank 2decreases extremely slightly but, in practice, this influence isextremely small, so that the following description will be made on theassumption that the suspension wire 3 is completely flexible. Asdescribed previously, the points A and B' on the tank 2 and those A andB on the gyro case 1 are held in alignment with each other by theoperation of the servo system, and consequently the tank 2 is alsoinclined at the angle 0 to the horizontal plane I-I-I-I' as is the casewith the gyro case 1. Assuming that no external acceleration exists, noexternal force acts in the direction of the spin axis of the gyro case1, so that the suspension wire 3 is aligned with the vertical line. Ifthe tensile force of the suspension wire 3 is taken as T and theresidual weight of the gyro case 1 except its buoyancy due to the damperliquid 7 is taken as mg, the tensile force T of the suspension wire 3provides about the point the following moment M: t

I M TrsinO mg r sin0 and this moment is applied as torque to the gyroabout its horizontal axis (passing through the point 0 and normal to thesheet of the drawing).'I-Iere, r represents the distance between thecenterO of gravity of the gyro case 1 and the coupling point Q of thesuspension wire 3 with the gyro case 1 as shown in the figure. Namely,also with this method, torque proportional to in a differential mannerand their output ends 16-1 are since this twisting torque isproportional to 6, it is prothe inclination of the spinaxisto thehorizontal plane can be applied to the gyro about its horizontal axis inexactly the same manner as in the case of the conventional gyrocompasses, so that a gyrocompass can be obtained by selectingthedistance r, the residual mass mg and the angular momentum of the gyroand selecting the period of its north-seeking motion in the rangeportional to the inclination angle 0 of the gyro spin axis, andconsequently it is possible to apply a damping ac tion to the gyro.

7 FIG. 1 1 shows a practical embodiment of the secondary coil 5N of, forexample, the north side of thedeviaof several tens minutes to onehundred and several tens minutes. In practice, this is equivalent tothat the distance r has become a little longer than the practicaldistance between 0, and Q on account of the flexural rigidity of thesuspension wire 3.

A description will be made of a damping device effective when used inthe gyrocompass described in connection with FIGS. 5 to 9. The basicprinciple of the damping device is that torque proportional to theinclination of the spin axis of the gyro from the horizontal plane isapplied to the gyro about its vertical axis, which principle has alreadybeen utilized in many conventional gyrocompasses. Where the spin axis ofthe t gyrocomp'ass'described previously in connection with a the gyro inthe gyro case I and the gyro case 1 moves by'O, 0 e in the direction ofB until the suspensionwire 3 comes to coincide with the vertical lineand then the gyro case 1 stands still. In other words, the inclinationangle 0 of the gyro and the amount of movement e of the gyro case 1 inthe direction of the spin axis relative to the tank 2 are completely inproportion to each other. Consequently, a desired damping action can beobtained by electrically detecting the amount of movement a, biasing thefollowing position of the vertical follow-up system in accordance withthe detected amount and twisting the suspension wire 3.

FIG. 10 illustrates a concrete embodiment with the above principle beingapplied to the FIG. 7 example. In the present embodiment, two coils 16-2and 16-3 are additionally provided on the north and south sides of thesecondary side coils 5N and 58 of the non-contact deviation detectingdevice 6 in such a manner that the faces of the bobbins of the coils16-2 and 16-3 may lie in parallel with the two pairs of coils SNE, SNWand SSE, SSW. The coils 16-2 and 16-3 are interconnected tion detectingapparatus shown in FIG. 10. In this embodiment, the coil 16-2 fordamping is disposed on the base plate to surround the four coils 111 to114 which are arranged in square as described with reference to FIG. 4.

According to this embodiment in which twocoils 16-2 and 16-3 for dampingare provided outside two secondary coils of the deviation detectingapparatus at the south and north positions of the tank, the inclinationangle of the spin axis relative to the-horizontal plane can be detectedwithout additionally providing any primary coil. Accordingly, it may beunderstood that the deviation detecting apparatus of the example can beused instead of an expensive accelerometersuch as, for example, anelectrolyte level or the like.

We claim as our invention:

1. A deviation detecting'apparatus comprising a primary coil forgenerating an alternating magnetic field,

and a secondary voltage inducting device disposed to dance with thealternating magnetic field caused by said primary coil, characterized inthat said secondary voltage inducing device consists of four secondarycoils, said four secondary coilsbeing arranged in a plane in the form ofa square and each of said four secondary coils being made up by windingtwo electrically insulated wiresin parallel, the two first wires ofadjacent two secondary coils of said four secondary coils beingconnected to deliver an output which isthe sum of voltages inducedtherein and to form two winding groups, said two winding groups beingconnected to deliver an output which is the difference of voltagesinduced therein, the two second wires of the other adjacent twosecondary coils being connected to deliver an output which is the sum ofvoltages induced therein and to form two other winding groups, said lastmentioned two winding groups being connected to deliver an output whichis the difference of voltages induced therein.

2. A deviation detecting apparatus as claimed in claim 1, whereinanother coil is providedwhich surrounds said four secondary coils.

i' i I l 10!

1. A deviation detecting apparatus comprising a primary coil forgenerating an alternating magnetic field, and a secondary voltageinducting device disposed to oppose said primary coil with a spacetherebetween and producing an induced secondary voltage in accordancewith the alternating magnetic field caused by said primary coil,characterized in that said secondary voltage inducing device consists offour secondary coils, said four secondary coils being arranged in aplane in the form of a square and each of said four secondary coilsbeing made up by winding two electrically insulated wires in parallel,the two first wires of adjacent two secondary coils of said foursecondary coils being connected to deliver an output which is the sum ofvoltages induced therein and to form two winding groups, said twowinding groups being connected to deliver an output which is thedifference of voltages induced therein, the two second wires of theother adjacent two secondary coils being connected to deliver an outputwhich is the sum of voltages induced therein and to form two otherwinding groups, said last mentioned two winding groups being connectedto deliver an output which is the difference of voltages inducedtherein.
 2. A deviation detecting apparatus as claimed in claim 1,wherein another coil is provided which surrounds said four secondarycoils.